1. Field of the Invention
The present invention relates to a temperature control system and a temperature control method for a hot nozzle used in a runner-less injection molding process of a plastic.
2. Description of the Prior Art
The applicant of the present application has proposed an improved hot nozzle in U.S. Pat. No. 4,648,833. The hot nozzle proposed in this U.S. patent does not require an external heater and can be rapidly heated or cooled in a short time. The nozzle includes a nozzle portion and a base portion. The nozzle portion is adapted to be inserted into a bore of a mold which is formed in communication with a mold cavity. The base portion serves to provide communication with the nozzle portion for the flow of molten resin injected from an injection molding machine. A pair of longitudinal slits extend over the length of the nozzle except a front end of the nozzle portion. Electric current is applied between both ends of the base portion divided by the slits, so that the nozzle portion is heated by itself.
However, in the practical application of the hot nozzle to the injection molding process, the front end of the nozzle is liable to be influenced by the temperature of the mold since the front end normally contacts the mold during the molding process. Further, the hot nozzle is formed of a relatively thin metal material and has a relatively small heat capacity. This may cause a temperature difference between the front end and a part of the nozzle on the side of the base portion. Particularly, when the mold is cooled to take out the molded product, the molten resin is solidified in the front end, so that no further injection process can be performed. Thus, the hot nozzle involves the problem that it is very difficult to control its temperature.